You can't send text messages from an iPad. You can send messages via imessage, whatsapp etc.
Edit: There is an app / wprk around you can use. Read here:
From what I can see, that won't allow you to use the free messages that you have.
It's a shame that MightyText isn't available for ios due to Apple restrictions. Android tablets utilise this for texting from their allowances.
Try looking for texting apps in iTunes.
Because "most" mobile broadband devices can send texts they include a hundred texts with the plans.
Unfortunately Apple didn't feel the need to include basic gsm features with their on board modem for iPad minis.
The only way is through a messaging app.
Or ...when I read about this last night @viridis it was talking about the need for an iPhone to work with the iPad so you can use Apples 'Continuity' programme with regards to sms....?? Seemed a roundabout way of achieving not much at all...
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